如何得到一个文件的大小 MB (兆字节) ？

小开

Try following code:

File file = new File("infilename");


// Get the number of bytes in the file
long sizeInBytes = file.length();
//transform in MB
long sizeInMb = sizeInBytes / (1024 * 1024);

小开

file.length() will return you the length in bytes, then you divide that by 1048576, and now you've got megabytes!

小开

You can retrieve the length of the file with File#length(), which will return a value in bytes, so you need to divide this by 1024*1024 to get its value in mb.

小开

最佳答案

Use the length() method of the File class to return the size of the file in bytes.

// Get file from file name
File file = new File("U:\intranet_root\intranet\R1112B2.zip");


// Get length of file in bytes
long fileSizeInBytes = file.length();
// Convert the bytes to Kilobytes (1 KB = 1024 Bytes)
long fileSizeInKB = fileSizeInBytes / 1024;
// Convert the KB to MegaBytes (1 MB = 1024 KBytes)
long fileSizeInMB = fileSizeInKB / 1024;


if (fileSizeInMB > 27) {
...
}

You could combine the conversion into one step, but I've tried to fully illustrate the process.

小开

public static long sizeOf(File file)

More info on API : http://commons.apache.org/proper/commons-io/apidocs/org/apache/commons/io/FileUtils.html

小开

Example :

public static String getStringSizeLengthFile(long size) {


DecimalFormat df = new DecimalFormat("0.00");


float sizeKb = 1024.0f;
float sizeMb = sizeKb * sizeKb;
float sizeGb = sizeMb * sizeKb;
float sizeTerra = sizeGb * sizeKb;




if(size < sizeMb)
return df.format(size / sizeKb)+ " Kb";
else if(size < sizeGb)
return df.format(size / sizeMb) + " Mb";
else if(size < sizeTerra)
return df.format(size / sizeGb) + " Gb";


return "";
}

小开

Since Java 7 you can use java.nio.file.Files.size(Path p).

Path path = Paths.get("C:\\1.txt");


long expectedSizeInMB = 27;
long expectedSizeInBytes = 1024 * 1024 * expectedSizeInMB;


long sizeInBytes = -1;
try {
sizeInBytes = Files.size(path);
} catch (IOException e) {
System.err.println("Cannot get the size - " + e);
return;
}


if (sizeInBytes > expectedSizeInBytes) {
System.out.println("Bigger than " + expectedSizeInMB + " MB");
} else {
System.out.println("Not bigger than " + expectedSizeInMB + " MB");
}

小开

Easiest is by using FileUtils from Apache commons-io.( https://commons.apache.org/proper/commons-io/javadocs/api-2.5/org/apache/commons/io/FileUtils.html )

Returns human readable file size from Bytes to Exabytes , rounding down to the boundary.

File fileObj = new File(filePathString);
String fileSizeReadable = FileUtils.byteCountToDisplaySize(fileObj.length());


// output will be like 56 MB

小开

You can use substring to get portio of String which is equal to 1 mb:

public static void main(String[] args) {
// Get length of String in bytes
String string = "long string";
long sizeInBytes = string.getBytes().length;
int oneMb=1024*1024;
if (sizeInBytes>oneMb) {
String string1Mb=string.substring(0, oneMb);
}
}

小开

You can use FileChannel in Java.

FileChannel has the size() method to determine the size of the file.

    String fileName = "D://words.txt";


Path filePath = Paths.get(fileName);


FileChannel fileChannel = FileChannel.open(filePath);
long fileSize = fileChannel.size();


System.out.format("The size of the file: %d bytes", fileSize);

Or you can determine the file size using Apache Commons' FileUtils' sizeOf() method. If you are using maven, add this to pom.xml file.

<dependency>
<groupId>commons-io</groupId>
<artifactId>commons-io</artifactId>
<version>2.6</version>
</dependency>

Try the following coding,

    String fileName = "D://words.txt";
File f = new File(fileName);


long fileSize = FileUtils.sizeOf(f);


System.out.format("The size of the file: %d bytes", fileSize);

These methods will output the size in Bytes. So to get the MB size, you need to divide the file size from (1024*1024).

Now you can simply use the if-else conditions since the size is captured in MB.

小开

Kotlin Extension Solution

Add these somewhere, then call if (myFile.sizeInMb > 27.0) or whichever you need:

val File.size get() = if (!exists()) 0.0 else length().toDouble()
val File.sizeInKb get() = size / 1024
val File.sizeInMb get() = sizeInKb / 1024
val File.sizeInGb get() = sizeInMb / 1024
val File.sizeInTb get() = sizeInGb / 1024

If you'd like to make working with a String or Uri easier, try adding these:

fun Uri.asFile(): File = File(toString())


fun String?.asUri(): Uri? {
try {
return Uri.parse(this)
} catch (e: Exception) {
}
return null
}

If you'd like to easily display the values as a string, these are simple wrappers. Feel free to customize the default decimals displayed

fun File.sizeStr(): String = size.toString()
fun File.sizeStrInKb(decimals: Int = 0): String = "%.${decimals}f".format(sizeInKb)
fun File.sizeStrInMb(decimals: Int = 0): String = "%.${decimals}f".format(sizeInMb)
fun File.sizeStrInGb(decimals: Int = 0): String = "%.${decimals}f".format(sizeInGb)


fun File.sizeStrWithBytes(): String = sizeStr() + "b"
fun File.sizeStrWithKb(decimals: Int = 0): String = sizeStrInKb(decimals) + "Kb"
fun File.sizeStrWithMb(decimals: Int = 0): String = sizeStrInMb(decimals) + "Mb"
fun File.sizeStrWithGb(decimals: Int = 0): String = sizeStrInGb(decimals) + "Gb"

小开

     String FILE_NAME = "C:\\Ajay\\TEST\\data_996KB.json";
File file = new File(FILE_NAME);


if((file.length()) <= (1048576)) {
System.out.println("file size is less than 1 mb");
}else {
System.out.println("file size is More  than 1 mb");
}

Note: 1048576= (1024*1024)=1MB output : file size is less than 1 mb

小开

You can do something like this:

public static String getSizeLabel(Integer size) {


String cnt_size = "0";
double size_kb = size / 1024;
double size_mb = size_kb / 1024;
double size_gb = size_mb / 1024;


if (Math.floor(size_gb) > 0) {
try {
String[] snplit = String.valueOf((size_gb)).split("\\.");
cnt_size = snplit[0] + "." + snplit[1].substring(0, 2) + "GB";
} catch (Exception e) {


cnt_size = String.valueOf(Math.round(size_gb)) + "GB";
}
} else if (Math.floor(size_mb) > 0) {
try {
String[] snplit = String.valueOf((size_mb)).split("\\.");
cnt_size = snplit[0] + "." + snplit[1].substring(0, 2) + "MB";


} catch (Exception e) {


cnt_size = String.valueOf(Math.round(size_mb)) + "MB";
}
} else {
cnt_size = String.valueOf(Math.round(size_kb)) + "KB";
}


return cnt_size;
}

How To use:

Integer filesize = new File("path").length();
getSizeLabel(filesize) // Output  16.02MB